1. Field of the Invention
The present invention relates to emulsions as cosmetic preparations which comprise 1,2-alkanediols and polar oil components. The compositions according to the present invention exhibit good sensory properties that result, among others, in improved in-vivo effectiveness.
2. Discussion of Background Information
The skin is our largest organ and at the same time the reflection of our soul. No other organ is so exposed to outside influences. Heat, cold or solar radiation, wrong or excessive cleansing of the skin, all of this stresses the skin.
Every day water evaporates via the surface of the skin. Internal and external factors additionally influence the degree of drying, such as hormonal influences, biological aging, disease and nutrition, light, environment and climate.
Normal skin and especially dry skin must therefore be supplied with moisture, lipids and optionally active ingredients. Healthy skin has different possibilities for keeping water loss to a minimum. It has so-called humectant factors, namely salts, various organic acids and urea. These factors take on the function of binding moisture and retaining it in the skin. The skin fats, lipids, are just as important. Only with the aid of this intact protective barrier is it possible for the upper layer of the skin to regulate the water content and additionally to ensure that infective agents such as bacteria, viruses or fungi and other harmful substances cannot penetrate the skin unhindered.
Dry skin is sensitive and mainly needs care. Cosmetic preparations such as creams and lotions primarily have the function of sustainably balancing the fat and moisture requirements of the skin, thus reestablishing the natural balance in the skin. It is therefore important to use preparations that contain in equal measure the skin-related lipids, humectants and active care ingredients. In addition, a care product also needs active ingredients that are able to bind water in the skin in the long term.
Lipids are fats and fatty substances. For cosmetics they are important primarily as emollient ingredients and as lipids that are present in the horny layer of the epidermis and that are stored between the horny cells. They enable the skin to store moisture. In addition to the skin care aspect, lipids are added to the cosmetic preparations in order to ensure it is easier to disperse them on the skin and in order to improve the sensory properties of the preparations.
As used in the present specification and the appended claims, the term “lipids” is used as a generic term for fats, oils, waxes and the like, said term being entirely commonplace to a person of skill in the art. Further the terms “oil phase” and “lipid phase” are used herein interchangeably.
Oils and fats differ from one another in their polarity, which is difficult to define. It has already been proposed to adopt the interfacial tension towards water as a measure of the polarity index of an oil or of an oil phase. The lower the interfacial tension between this oil phase and water, the greater the polarity of the oil phase in question. According to the present invention, the interfacial tension is regarded as one possible measure of the polarity of a given oil component.
The interfacial tension is the force which acts on an imaginary line one meter in length at the interface between two phases. The physical unit for this interfacial tension is conventionally calculated from the force/length relationship and is usually expressed in mN/m (millinewtons divided by meters). It has a positive sign if it tends to reduce the interface. In the converse case, it has a negative sign. For the purposes of the present invention, lipids are regarded as polar if their interfacial tension towards water is less than about 20 mN/m, and as nonpolar if their interfacial tension towards water is more than about 30 mN/m. Lipids with an interfacial tension towards water between about 20 and about 30 mN/m are generally referred to as moderately polar.
EP 655904 generally describes the use of alkane diols with 5 to 10 carbon atoms in cosmetic products and in particular their skin-moisturizing effect.
DE 10341179 discloses deodorant compositions with a combination of alkane-1,2-diols and α- and/or β-hydroxyacids. The antibacterial effect of alkane-1,2-diols is also known. JP 2002/2003330 thus describes the antibacterial effect of a combination of alkane-1,2-diols and ascorbic acid esters. WO 03/000220 describes the use of 1,2-decanediol against bacteria causing body odor. U.S. Pat. No. 6,123,953 describes the use of alkane-1,2-diols for inactivating skin microorganisms by the use of 1,2-octanediol.
Emulsions, here in particular W/O, O/W or W/O/W emulsions, are often used as cosmetic or medical preparations. Emulsions are generally understood as meaning heterogeneous systems which comprise two liquids which are immiscible or only miscible with one another to a limited extent, which liquids are normally referred to as phases. In an emulsion, one of the two liquids (W/O) is dispersed in the other liquid in the form of very fine droplets.
If the two liquids are water and oil and if oil droplets are finely distributed in water, then this is an oil-in-water emulsion (O/W emulsion, e.g., milk). The basic character of an O/W emulsion is determined by the water. In the case of a water-in-oil emulsion (W/O emulsion, e.g., butter), the principle is reversed, the basic character here being determined by the oil.
One skilled in the art is naturally aware of a plurality of possibilities for formulating stable emulsion preparations for cosmetic or dermatological application, e.g., in the form of creams and ointments that are spreadable in the range of room temperature to skin temperature, or as lotions and milks, that are rather flowable in this temperature range.
A plurality of lipids are known from DE 1001921 that as an addition to W/O emulsions have better sensory properties, such as, e.g., ease of distribution on the skin or the ability to be absorbed by the skin.
However, the problem with all the preparations is to produce stable emulsions with a predominantly polar oil phase without any losses in terms of sensory properties.
In the prior art, attempts to solve this problem of the interfacial activity of the lipids are made by adding suitable thickener systems, which, in turn, results in the referenced disadvantages in terms of the sensory properties of the cosmetic preparation.
Thus in DE 198 55 153, DE 199 24 277, DE 100 48 125, DE 100 48 366, DE 100 48 427, DE 100 48 429 and in DE 100 48 683 it is mentioned that preparations in combination with very polar oils, such as, e.g., the vegetable oils which are frequently used in commercial products, have the disadvantage that they are unstable or are limited to a narrow field of application or to a very limited selection of materials.
It would be advantageous to have available stable emulsions and in particular cosmetic preparations that contain predominantly polar oil components.